Laminated plastic cards are widely employed as certificates of citizenship, identification cards, passports, driver's licenses, and the like. They generally consist of a paper or plastic film with descriptive information, such as the name, residence, title, or the like, of the holder of the card printed thereon and a photograph of the holder pasted thereon. The upper or lower surface of the card, or both, is covered by a plastic film.
Since these certificates are often the target of forgery, various efforts have been used to make such forgery more difficult.
One method of preventing forgery of a laminated plastic card is the replacement of the photograph with an image created by electronic graphic technology. In accordance with this technique, descriptive and graphic information are stored in an electronic memory device and printed on a sheet of paper by a videoprinter that is based on the thermal transfer printing system. The ink used in this printing system contains one or more volatile dyes that are sublimed by heating and transferred to a substrate, e.g., paper, a polyester resin film, or an ethylene-vinyl acetate resin film. The upper or lower surface, or both, of the substrate is covered by one or more transparent plastic films of polyethylene terephthalate or polycarbonate. Ethylene ethyl acrylate or ethylene-vinyl acetate is employed to adhere the film of polyethylene terephthalate or polycarbonate to the surface of the videoprint.
An example of a laminated plastic card that is available in the prior art is shown in FIG. 1. A lamination 10 comprises a dye accepting layer 5 of a polyester resin or an ethylene-vinyl acetate resin, a substrate 6 of paper or synthetic paper, and a back coat layer 7 of an acrylate resin. The dye accepting layer accepts and firmly fixes one or more dyes sublimed from a volatile dye mixture, and the back coat layer 7 allows control of the feeding of the lamination 10 in a videoprinter. The videoprinter is employed to print patterns 8 containing descriptive and graphic information by a thermal transfer printing system with which one or more dyes sublimed from a volatile dye is transferred to the dye accepting layer 5. A transparent plastic film 1 of polyethylene terephthalate or polycarbonate is adhered on the lamination 10 by an adhesive agent of ethylene ethyl acrylate or ethylene-vinyl acetate. A hardened adhesive layer is illustrated as 2.
A laminated plastic card produced in this manner is effective in preventing forgery because all of the visible information is printed in one plane on the same sheet.
These known cards, however, suffer from the disadvantage that the dye migrates from the dye accepting layer into the adhesive layer. As a result, the picture and description diffuse to become illegible. In addition, ethylene ethyl acrylate and ethylene-vinyl acetate do not strongly adhere to a dye accepting layer of polyester resins or ethylene-vinyl acetate resins. This allows a plastic film of polyethylene terephtalate or polycarbonate to be readily peeled from the dye accepting layer of polyester resins or ethylene-vinyl acetate resins and employed to cover another videoprint prepared for the purpose of forgery.